When operating unthrottled (e.g., without a throttle or at or near wide-open throttle) in an electric valve actuation type engine (or a continuously variable valve lift engine), a mass airflow sensor is degraded due to reverse flow effects leading to erroneous measurement. A manifold pressure sensor (MAP) also cannot be the primary sensor for measuring airflow (e.g., using a speed density approach), as the manifold pressure is substantially near atmospheric pressure during a wide variety of engine conditions. Further, even sensors that provide directional compensation may not be functional at low loads for these engines.
The inventors herein have recognized one approach to overcome these disadvantages. In particular, that is to estimate airflow using engine speed, temperature, and valve timing (additional compensation from an estimate, or measurement, of atmospheric pressure can be used if desired (e.g., from a MAP during engine starting)). But, as the engine ages, this estimate can become degraded. In other words, the engine air-to-fuel ratio control performance can be significantly degraded due to aging and part-to-part variability.
As such, the inventors herein have developed a system to compensate for such effects. The system comprises: an engine with electronically adjustable engine valve timing or valve lift; a sensor coupled to said engine; and a controller for: determining whether a condition is present; when said condition is present, operating in a first mode where an engine air amount is determined based on a valve amount and an adaptive parameter, wherein during said first mode said controller further updates said adaptive parameter based on said sensor; and operating in a second mode where said engine air amount is determine based on said valve amount and said adaptive parameter.
In this way, it is possible to utilize the adaptive information across multiple engine operating modes, and even in modes where adaptation is not possible or where adaptation is limited.